The present invention to a method and a machine for forming an end portion of a plastic pipe.
It is previously known to provide an end portion of a plastic pipe with a sealing ring positioned in an internal groove in the pipe end portion by transferring the pipe end portion into a softened state and by introducing the sealing ring into the softened pipe end portion by relative movement between the sealing ring and the pipe end portion. Thereby, the sealing ring acts as a mould element for forming the groove for the sealing ring which after the forming operation is left in the groove in a locked-in position. When conducting the described forming operation the sealing ring is in a first operational step positioned on a mandrel on which the sealing ring is axially fixed by means of a support sleeve. The softened pipe end portion is then pushed over the mandrel and over the sealing ring which is axially fixed on the mandrel. Thereby, the softened pipe end portion conforms to the peripheral surface of the mandrel previously covered by the support sleeve, whereupon the pipe end portion is transferred to a solid state by cooling and is removed from the mandrel with the sealing ring remaining in the groove formed by the ring itself.
Previously known methods for forming an end portion of a plastic pipe in which a sealing ring is located in the end portion of the pipe comprise rather many operational steps and are time consuming. Thus, there are required several forming machines for matching an extruder in which the plastic pipes are manufactured.
Another drawback of the prior art methods is the difficulty of avoiding deformation of the pipe end portion and the adjacent section of the pipe when the softened pipe end portion is pushed over the mandrel and the sealing ring positioned thereon. Thus, the forming unit consisting of the mandrel and the sealing ring provides a relatively great resistance against the axial pushing movement in turn requiring that relatively great axial forces are exerted on the pipe. This may cause that the pipe wall is deformed for example to a corrugated shape.